Chemokines (chemoattractant cytokines) are a family of structurally and functionally related small proteins that direct migration of cells (e.g., leukocytes and/or lymphocytes and/or stem cells and/or neurons) in addition to controlling other biological processes, such as angiogenesis, morphogenesis, autoimmunity, tumor growth and metastasis. Chemokines are grouped into families based on the presence and relative position of amino terminal cysteine residues (e.g. CC, CXC, CX3C and C chemokines). Generally, the biological activity of a chemokine is mediated by a cell surface receptor, in particular a 7-transmembrane-domain G protein-coupled receptor (GPCR). The chemokine receptors are grouped and named according to the family of chemokine(s) to which they bind.
One member of the CXCR family is CXCR4 that is predominantly expressed on lymphocytes and that activates chemotaxis. CXCR4, also called fusin, is an alpha-chemokine receptor specific for stromal-derived-factor-1 (SDF-1, also called CXCL12), a molecule endowed with potent chemotactic activity for lymphocytes.
CXCR4 plays a role in embryogenesis, homeostasis, fibrosis and inflammation. The CXCR4/SDF-1 pathway has been implicated in organ vascularisation, as well as in the immune and hematopoietic systems (Tachibana K et al. (1998) Nature 393:591-594). Drugs that block the CXCR4 receptor appear to be capable of “mobilising” hematopoietic stem cells into the blood stream as peripheral blood stem cells. CXCR4 has also been shown to function as a co-receptor for T lymphorophic HIV-1 isolates (Geng Y et al. (1996) Science 272:872-877). CXCR4 has also been shown to be expressed on a wide variety of cancer cell types and to be involved in stimulating the metastatic process in many different neoplasms (Murphy P M (20001) N. Eng. J. Med. 345:833-835).
G-protein coupled receptors are currently the most important class of therapeutic targets, and antibodies directed against them are highly sought for therapeutic, diagnostic and research purposes. Despite substantial interest in these targets, high-quality antibodies or binding agents against membrane proteins have been challenging to generate using conventional means.
Binding agents to CXCR4 have previously been described, including whole antibodies (e.g. Medarex), antibody fragments and single-domain antibodies (Ablynx), however the present binding agents provide an alternative construct which alleviates some of the drawbacks of antibodies, for example, Fc-mediated effects as well as high production costs, low stability and their large size, which reduce their utility for tumor penetration. The binding agents of the present invention provide an alternative to small molecule agents such as Plerixafor (Mozobil or AMD3100) which is currently indicated for peripheral blood stem cell mobilisation in combination with granulocyte colony stimulating factor (G-CSF) in patients with non-Hodgkins' lymphoma (NHL) and multiple myeloma (MM).